Accounting is based on either the cash basis or the accrual basis. In cash basis accounting, companies record revenues when they receive the cash and they record expenses when the cash is paid. In accrual basis accounting, companies record revenues when they perform services (rather than when they receive cash) and record expenses when they are incurred (rather than when paid). The time-period concept assumes that unlimited economic life of a company will be divided into regular intervals and that financial statements will be prepared for specific periods such as a month, quarter, or year. Accounting periods may be monthly, quarterly, semiannually or yearly.